Digital speaker driving apparatus

ABSTRACT

A digital sound system suitable for a digital speaker device for directly converting analog sound by a circuit using a ΔΣ modulator and a mismatch shaping filter circuit to output a plurality of digital signals and a plurality of speakers driven by the plurality of digital signals. A digital speaker driving device includes a ΔΣ modulator, a post filter, s driving circuits, and a power supply circuit to supply power to the ΔΣ modulator, the post filter and the s driving elements and the s driving circuits are adapted to s digital signal terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application, under 35 U.S.C. §111(a),of International application No. PCT/JP2009/059867, filed on May 29,2009, which claimed priority to Japanese application Nos. 2008-156284,filed on Jun. 16, 2008, 2008-314438, filed on Dec. 10, 2008,2008-314905, filed on Dec. 10, 2008 and 2008-314929, filed on Dec. 10,2008, the disclosures of which are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention is related to a digital speaker driving apparatus,a digital speaker apparatus, an actuator, a flat display apparatus, anda mobile electronic device. Specifically, the present invention isrelated to a digital acoustic system and applications thereof in which adigital speaker apparatus which directly converts a digital signal intoan analog audio is used.

2. Description of the Related Art

The digital speaker technology which directly converts a digital signalinto an analog audio has been proposed.

In WO2007/135928A, a method is shown in which an analog audio isdirectly converted with a circuit inputting two digital audio signals X(L) and Y (R) and outputting a plurality of digital signals, the circuitcomprising a ΔΣ modulator and a miss-match shaping filter circuit, and aplurality of speakers driven by the plurality of digital signals or aplurality of driving elements.

In addition to having a characteristic of low power consumption comparedto an analog speaker apparatus driven by an analog electric signal,because a plurality of speaker elements or plurality of driving elements(coils etc) are used, such a digital speaker apparatus, which directlyconverts a digital signal into an analog audio by using the digitalspeaker technology, can produce a large sound pressure at a low drivingvoltage, compared to a speaker which uses a conventional one speakerelement or single driving element driven by an analog electric signal.

However, because it is presumed that an analog signal is input in aconventional speaker apparatus, it is necessary to convert the inputanalog signal into a digital signal in order to integrate a digitalspeaker apparatus into a conventional digital acoustic system, asignificant problem arises when realizing a digital acoustic systemwhich uses a digital speaker apparatus.

Typical examples of digital acoustic systems which use conventionalanalog speaker apparatuses are shown in FIG. 1 a to FIG. 1 c. FIG. 1 ashows a first embodiment of a digital acoustic system which uses adigital signal source and an analog speaker apparatus. In this example,a signal from the digital signal source is converted to an analog signalby a D/A convertor and the signal is input to an analog speakerapparatus after the amplitude of the signal is amplified by an analogamplifier. This embodiment is best suited to an acoustic system whichuses a conventional analog amplifier and a speaker.

FIG. 1 b shows a second embodiment of a digital acoustic system whichuses a digital signal source and an analog speaker apparatus. In thisexample, a digital signal from a digital signal source is converted toan analog signal by a D/A convertor and input to an amplifier. In theamplifier, after the input analog signal is once converted to a digitalsignal by an A/D convertor, the signal is PWM modulated and theamplitude digitally amplified (D-class amplification) and then convertedback to an analog signal by the D/A convertor (usually an LC filter) andinput to an analog speaker apparatus. It is a more complex systemcompared with FIG. 1 a, however, the digital amplitude amplification(D-class amplification) has higher power efficiency and the amplifiercan operate with less power and with smaller space compared to an analogamplifier and therefore has become gradually used in recent years.

FIG. 1 c shows a third embodiment of a digital acoustic system whichuses a digital signal source and an analog speaker apparatus. In thisexample, a signal from the digital single source is input directly as adigital signal to an amplifier. In the amplifier, after the input signalis PWM modulated, the signal is converted to an analog signal by a D/Aconvertor (usually an LC filter) after the amplitude of the signal isdigitally amplified (D-class amplification) and input to an analogspeaker apparatus. In a digital device such as a personal computer or amobile phone, a digital signal source and an amplifier for the internetor data transmission are often arranged within the same device and thistype of system is being widely used.

In FIG. 1 b and FIG. 1 c, after the amplitude is digitally amplified(D-class amplification), a signal is converted to an analog signal by aD/A convertor (usually an LC filter) and input to an analog speakerapparatus, however, the digital amplitude amplification must be donewith a high voltage in order to output a large sound pressure, a digitalamplitude amplification semiconductor device which uses a high voltagespecial semiconductor technology is required and it is difficult tolower costs. In addition, when digital amplitude amplification isperformed with a high voltage, electromagnetic irradiation becomes largeand additional costs are incurred in order to reduce thiselectromagnetic irradiation.

In these conventional examples, because an analog signal is used as asignal input to a speaker apparatus, it is necessary to convert theanalog signal which is input to the speaker apparatus to a digitalsignal when a digital speaker apparatus which uses a circuit whichoutputs a plurality of digital signals by a ΔΣ modulator and amiss-match shaping filter circuit as disclosed in WO2007/13528A1, and aplurality of speakers driven by a plurality of digital signals is used,and therefore an A/D convertor must be further added to realize thedigital speaker apparatus and the power consumed by the newly requiredA/D convertor increases and the digital speaker apparatus becomescomplex. In addition, there is a problem in which a deterioration insound quality between an analog signal and a digital signal in the A/D(D/A) convertor between the digital signal source and the digitalspeaker apparatus can not be avoided.

BRIEF SUMMARY

The present invention discloses a digital acoustic system appropriatefor a digital speaker apparatus which directly converts into an analogaudio, the digital acoustic system including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a miss-match shapingfilter circuit, and one or a plurality of speakers which are driven bythe plurality of digital signals.

In one embodiment of the present invention, a digital speaker drivingapparatus which drives a digital speaker having s number of digitalsignal terminals is disclosed including a ΔΣ modulator which modulates adigital input signal and outputs an n bit digital signal; a post filterwhich is connected to the ΔΣ modulator and outputs an m bit digitalsignal obtained by miss-match shaping the n bit digital signal; numberof driving circuits to each of which one part of the m bit digitalsignal is input and each of which outputs a digital signal; and whereinthe s number of driving circuits correspond to the s number of digitalsignal terminals.

In addition, it is preferred that by supplying a variable voltage to thes number of driver elements by a power circuit arranged on the digitalspeaker driving apparatus, the amplitude of an output of a digitalsignal of the s number of driver circuits is adjusted. Furthermore, itis preferred that a digital attenuator be included which adjusts thevolume of a digital speaker by inputting a digital input signal to theΔΣ modulator after performing a calculation process. Furthermore, it ispreferred that a power circuit be controlled according to a digitalinput signal.

In one embodiment of the present invention, a digital speaker drivingapparatus which is connected to a digital signal terminal of a digitalspeaker is disclosed having a first output circuit connected to a firstinput terminal of the digital terminals of the digital speaker; and asecond output circuit connected to a second input terminal of thedigital terminals of the digital speaker, the second input terminalforming a pair with the first input terminal; wherein the first outputcircuit and the second output circuit are input with signals, thesignals being inversed with each other.

Furthermore, it is preferred that the first output circuit and thesecond output circuit output signals of a first voltage, a secondvoltage, or a third voltage, in the case where the first output circuitoutputs the first voltage and the second output circuit outputs thethird voltage, the state of the digital signal output is in a firststate, in the case where the first output circuit outputs the thirdvoltage and the second output circuit outputs the first voltage, thestate of the digital signal output is in a second state, and in the casewhere both of the first output circuit and the second output circuitoutput the second voltages, the state of the digital signal output is ina third state.

Furthermore, in the digital speaker driving apparatus stated above, itis preferred that the ΔΣ modulator, the post filter, and the s number ofdriving circuits are formed on a single semiconductor or are sealed in asingle package.

In one embodiment of the present invention, a digital speaker apparatusincludes a digital speaker having a plurality of input terminals; and adigital speaker driving circuit which is connected to the inputterminals and drives the digital speaker; wherein the digital speakerdriving circuit is arranged just behind coils of the digital speaker.

In one embodiment of the present invention, a digital speaker apparatusis disclosed including a ΔΣ modulator which modulates a digital inputsignal and outputs an n bit digital signal; a post filter which isconnected to the ΔΣ modulator and outputs an m bit digital signalobtained by miss-match shaping the n bit digital signal; s number ofdriving circuits to each of which one part of the m bit digital signalis input and each of which outputs a digital signal; s number of speakerdriving elements each of which is driven by a corresponding drivingcircuit among the s number of driving circuits; and r number ofvibration membranes which are driven by the s number of drivingelements; wherein s and r are 2 or more.

In one embodiment of the present invention, a digital speaker apparatusis disclosed including a ΔΣ modulator; and a digital speaker; whereinthe digital speaker has a plurality of coils each of which is driven bya different digital signal and all of which vibrate a common vibrationmembrane.

It is preferred that the plurality of coils are bound together andwound.

In one embodiment of the present invention, a digital actuator isdisclosed having a magnetostrictor, and a plurality of coils which areeach driven by different digital signals and which generate a magneticfield to the magnetostrictor.

In one embodiment of the present invention, a digital speaker apparatusis disclosed including a ΔΣ modulator which modulates a digital inputsignal and outputs an n bit digital signal; a post filter which isconnected to the ΔΣ modulator and outputs an m bit digital signalobtained by miss-match shaping the n bit digital signal; s number ofdriving circuits to each of which one part of the m bit digital signalis input and each of which outputs a digital signal; and s number ofelectrostatic elements each of which is driven by a correspondingdriving circuit among the s number of driving circuits.

In the digital speaker apparatus stated above, it is preferred that theΔΣ modulator, the post filter, and the s number of driving circuits andthe s number of electrostatic elements are formed on a single substrate.

In one embodiment of the present invention, a digital speaker drivingapparatus which drives a digital speaker having s number of digitalsignal terminals is disclosed including a ΔΣ modulator which modulates adigital input signal and outputs an n bit digital signal; a post filterwhich is connected to the ΔΣ modulator and outputs an m bit digitalsignal obtained by miss-match shaping the n bit digital signal; adigital delay control circuit which delays the m bit digital signal andoutputs the delayed m bit digital signal; s number of driving circuitsto each of which one part of the m bit digital signal is input and eachof which outputs a digital signal; wherein a delay time period of thedigital delay control circuit is controlled for each output according toa control signal.

In one embodiment of the present invention, a flat display apparatus isdisclosed including a flat display; a plurality of digital speakerswhich are arranged in a line on at least one side of the flat display;and a delay control circuit which controls the delay time periods ofdriving signals supplied to the plurality of digital speakers accordingto a control signal.

In one embodiment of the present invention, a digital speaker apparatusis disclosed including a port for connecting to a portable digital audiosource apparatus; a circuit for processing the digital signals input tothe port in a digital format; and a digital speaker driven by thecircuit; wherein the digital speaker apparatus operates with a battery.

In one embodiment of the present invention, a mobile electronic deviceis disclosed including a digital speaker; and a driving apparatus whichdrives the digital speaker without converting a digital signal to ananalog signal; wherein the portable electronic device operates with abattery.

In one embodiment of the present invention, a mobile electronic deviceis disclosed including a port for connecting to a portable digital audiosource apparatus; a driving apparatus for processing the digital signalsinput to the port in a digital format; and a digital speaker driven bythe driving apparatus; wherein the portable electronic device operateswith a battery.

In one embodiment of the present invention, a digital speaker apparatusis disclosed including a digital speaker; a digital speaker drivingapparatus for processing a digital signal without converting the digitalsignal to an analog signal; and a microphone; wherein the digitalspeaker driving apparatus operates so that a noise is cancelled based ona signal from the microphone.

In one embodiment of the present invention, a mobile electronic deviceis disclosed including a wireless receiver receiving a digital signal; adigital speaker driving apparatus which generates a plurality of digitalsignals without converting the digital signal output by the wirelessreceiver to an analog signal; and a digital speaker which is driven bythe plurality of digital signals.

In addition, in one embodiment of the present invention, a digitalspeaker system which drives a digital speaker including s number ofgroups of a digital signal terminal arranged with a group including afirst input terminal and a second input terminal is disclosed includinga ΔΣ modulator which modulates a digital input signal and outputs an nbit digital signal; a post filter which is connected to the ΔΣ modulatorand outputs an m bit digital signal obtained by miss-match shaping the nbit digital signal; and s number of driving circuits each of whichcorresponds to one of the s pairs of digital input terminals and to eachof which one part of the m bit digital signal is input and each of whichoutputs a digital signal; wherein each of s number driving circuits hasa first output circuit connected to a first input terminal of acorresponding digital input terminal and a second output circuitconnected to a second input terminal which forms a pair with the firstinput terminal of a corresponding digital input terminal; and whereinthe driving circuit has at least three states of digital signal outputaccording to the combination of a first digital signal input to thefirst output circuit and a second digital signal input to the secondoutput circuit.

In addition, in one embodiment of the present invention, a digitalspeaker apparatus which drives a plurality of digital speakers includings number of digital signal terminals respectively is disclosed includinga ΔΣ modulator which modulates a digital input signal and outputs an nbit digital signal; a post filter which is connected to the ΔΣ modulatorand outputs an m bit digital signal obtained by miss-match shaping the nbit digital signal; a digital delay control circuits which delays the mbit digital signal and outputs the delayed m bit digital signal; snumber of driving circuits to each of which a part of the delayed m bitdigital signal is input and each of which outputs a digital signal; anda sensor which senses information related to a person or an object whichexists in a periphery; wherein a delay time period of the digital delaycontrol circuit is controlled according to a control signal generatedbased on the information sensed by the sensor, and the directionality ofaudio played back by the plurality of digital speakers is controlled toa direction or position of the person or the object detected by thesensor.

In addition, in one embodiment of the present invention, a digitalspeaker driving apparatus which drives a digital speaker having s numberof digital signal terminals is disclosed including a ΔΣ modulator whichmodulates a digital input signal and outputs an n bit digital signal; apost filter which is connected to the ΔΣ modulator and outputs an m bitdigital signal obtained by miss-match shaping the n bit digital signal;a digital delay control circuit which delays the m bit digital signaland outputs the delayed m bit digital signal; s number of drivingcircuits to each of which a part of the delayed m bit digital signal isinput and each of which outputs a digital signal; and a microphone whichdetects a sound in a periphery; wherein an audio of an opposite phase tothe sound detected by the microphone is generated by the digitalspeaker.

In this case, another digital speaker may be arranged, and the digitalspeaker driving apparatus may include a plurality of digital speakers,wherein the digital delay control circuit outputs an m bit digitalsignal which is delayed for each digital speaker by controlling thedelay time period of the m bit digital signal input.

Furthermore, one embodiment of a digital acoustic system using a digitalsignal source and a digital speaker apparatus of the present inventionis shown in FIG. 1 d. In the present invention, the signal of a digitalsignal source is input to the digital speaker apparatus as a digitalsignal. The digital speaker apparatus directly converts an input digitalsignal to analog audio without converting to an analog signal.

According to the present invention, it becomes possible to reduce thecosts of the digital acoustic system because it is possible tomanufacture a digital acoustic system by combining with a simpleapparatus compared to a conventional analog acoustic system withoutlosing low power consumption characteristics which are the originalcharacteristics of a digital speaker. It is possible to reduce the costsof a digital speaker driving apparatus, which is required for thedigital acoustic system, because a large sound pressure with a lowdriving voltage is possible in the digital speaker apparatus, andbecause it is not necessary to use any special semiconductor technologyfor handling a high voltage in the case where a digital signal processcircuit is formed monolithically on a semiconductor. It is possible toreduce costs for suppressing electromagnetic irradiation becauseelectromagnetic irradiation (EMI) is small due to driving with a lowdriving voltage. It is possible to avoid a deterioration in soundquality because there is no A/D (D/A) convertor between a digital signalsource and a digital speaker apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is an exemplary diagram of a structure of a digital acousticsystem.

FIG. 1 b is an exemplary diagram of a structure of a digital acousticsystem.

FIG. 1 c is an exemplary diagram of a structure of a digital acousticsystem.

FIG. 1 d is a structural diagram of a digital acoustic system related toone embodiment of the present invention.

FIG. 1 e is a structural diagram of a digital acoustic system related toone embodiment of the present invention.

FIG. 2 a is a structural diagram of a power circuit of a digitalacoustic system related to a first embodiment of the present invention.

FIG. 2 b is a structural diagram of a power circuit of a digitalacoustic system related to a second embodiment of the present invention.

FIG. 2 c is a structural diagram of a power circuit of a digitalacoustic system related to a third embodiment of the present invention.

FIG. 3 a is a structural diagram of a speaker driving circuit of adigital acoustic system related to one embodiment of the presentinvention.

FIG. 3 b is a structural diagram of a speaker driving circuit of adigital acoustic system related to another embodiment of the presentinvention.

FIG. 4 a is a structural diagram of a digital acoustic system related toa fourth embodiment of the present invention.

FIG. 4 b is a structural diagram of a digital acoustic system related toa fourth embodiment of the present invention.

FIG. 5 is a structural diagram of a digital acoustic system related to afifth embodiment of the present invention.

FIG. 6 is a structural diagram of a digital acoustic system related to asixth embodiment of the present invention.

FIG. 7 is a structural diagram of a digital acoustic system related to aseventh embodiment of the present invention.

FIG. 8 a is a structural diagram of a digital acoustic system related toan eighth embodiment of the present invention.

FIG. 8 b is a structural diagram of a digital acoustic system related toan eighth embodiment of the present invention.

FIG. 8 c is a structural diagram of a digital acoustic system related toan eighth embodiment of the present invention.

FIG. 9 a is a structural diagram of a digital acoustic system related toa ninth embodiment of the present invention.

FIG. 9 b is a structural diagram of a digital acoustic system related toa ninth embodiment of the present invention.

FIG. 10 is a structural diagram of a digital acoustic system related toa tenth embodiment of the present invention.

FIG. 11 is a structural diagram of a digital acoustic system related toan eleventh embodiment of the present invention.

FIG. 12 is a structural diagram of a digital acoustic system related toa twelfth embodiment of the present invention.

FIG. 13 is a structural diagram of a digital acoustic system related toa thirteenth embodiment of the present invention.

FIG. 14 is a structural diagram of a digital acoustic system related toa fourteenth embodiment of the present invention.

FIG. 15 a is a structural diagram of a digital acoustic system relatedto a fifteenth embodiment of the present invention.

FIG. 15 b is a structural diagram of a digital acoustic system relatedto a fifteenth embodiment of the present invention.

FIG. 16 is a structural diagram of a digital acoustic system related toa sixteenth embodiment of the present invention.

FIG. 17 a is a structural diagram of a digital acoustic system relatedto a seventeenth embodiment of the present invention.

FIG. 17 b is a structural diagram of a speaker driving circuit includinga 3 level switching amplifier related to one embodiment of the presentinvention.

FIG. 18 is a structural diagram of a digital acoustic system related toan eighteenth embodiment of the present invention.

FIG. 19 is a structural diagram of a digital acoustic system related toa nineteenth embodiment of the present invention.

FIG. 20 is a structural diagram of a digital acoustic system related toa twentieth embodiment of the present invention.

FIG. 21 a is a structural diagram of a digital acoustic system relatedto a twenty-first embodiment of the present invention.

FIG. 21 b is structural diagram of a centralized control apparatus(2105) and in-car LAN, which transmits a digital signal, related to oneembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention are explained below withreferences to the drawings. Furthermore, the invention is not limited tothese embodiments. The present invention can be achieved with variousmodifications to the embodiments below based on technologies related tothe invention.

First Embodiment

FIG. 1 e shows a first embodiment of a digital speaker apparatus systemincluding a circuit for outputting a plurality of digital signals by aΔΣ modulator and a post filter circuit, and a plurality of speakerdriving elements. A 1 bit digital input signal (210) is input to a ΔΣmodulator (201) and converted to a plurality of n bit digital signals(211) by the ΔΣ modulator (201). The plurality of n bit digital signalsare converted to m bit digital signals (212) which have been miss-matchshaped by a post filter (202). The m bit digital signals (212) drive snumber of driving elements (2041-204 s) by speaker driving circuits(2031-203 s) and an analog audio is directly converted by a vibrationmembrane (213). The ΔΣ modulator (201), the post filter (202), thespeaker driving circuits (2031-203 s), and a power supply circuit (205)which supplies power to these circuits are structural components of adigital speaker apparatus (200).

Furthermore, it is possible for each of the digital signals input to thes number of speaker driving circuits (2031-203 s) to be at the samelevel at a certain moment. However, it is possible that a change in eachof the digital signals input to the s number of speaker driving circuits(2031-203 s) during a sufficiently long period of time is not the same.In this way, it is possible to reduce the consumption of wasteful powerby the driving elements (2041-204 s). For example, in the case where thesame digital signal is input to a number n of s speaker driving circuits(2031-203 s), the power larger by n times than the power which iswastefully consumed by each driving element is wastefully consumed isprevented. This can also be said concerning the other embodiments.

The internal structure of the power supply circuit (205) in the firstembodiment is shown in FIG. 2 a. A power source (251) from an externalpower source or a battery has a plurality of regulator circuits(2521-252 n) and is supplied to the ΔΣ modulator (201), the post filter(202), and speaker driving circuits (2031-203 s) via supply lines(2531-253 n). The regulator circuit (252 a) which supplies a power tothe speaker driving circuits (2031-203 s) can have a means (254) forvarying a supply voltage. In this way, it is possible to adjust theamplitude of a digital signal which drives a digital speaker and it ispossible to adjust the volume of the digital speaker.

Second Embodiment

FIG. 2 b shows a second embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. In the present embodiment, in order to adjust the volume of adigital speaker, the volume is digitally adjusted from a 1 bit digitalinput signal (210) input to the digital speaker apparatus, even thoughthe regulator circuit (252 a) which supplies a power for the speakerdriving circuits (2031-203 s) is not equipped with a means (254) forvarying a supply voltage.

Third Embodiment

FIG. 2 c shows a third embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. In the present embodiment, in order to adjust the volume of adigital speaker, the volume is digitally adjusted based on informationof a 1 bit digital input signal (210) input to the digital speakerapparatus, as a means (210) for varying a supply voltage of theregulator circuit (252 a) which supplies a power for the speaker drivingcircuits (2031-203 s).

When each of the speaker driving circuits (2031-203 s), which are shownin FIG. 2 a to FIG. 2 c, is 2-valued (−1, 1), it is possible to have s+1levels as a digital speaker driving state. In this case, m=s and therelationship 2n>(s+1) is satisfied in the ΔΣ modulator. An embodiment ofa speaker driving circuit (300 a) which has a 2-valued driving state isshown in FIG. 3 a. Two types of switch circuit including a PMOS element(301) and an NMOS element (302) are each connected to a speaker drivingelement (204) via an output terminal. An input signal A which is the2-valued digital signal is connected to the input of one of the switchcircuits via an inverter circuit (303). The speaker driving circuit (300a) has a 2 valued state (−1, 1) according to the state of the inputsignal A.

When each of the speaker driving circuits (2031-203 s), which is shownin FIG. 2 a to FIG. 2 c, is 3 valued (−1, 0, 1), it is possible to have2×s+1 levels as a digital speaker driving state. In this case, m=2×s andthe relationship 2n>(2×s+1) is satisfied in the Δ Σ modulator. Anembodiment of a speaker driving circuit (300 b) which has a 3-valueddriving state is shown in FIG. 3 a. Two types of switch circuitincluding a PMOS element (301) and an NMOS element (302) are eachconnected to a speaker driving element (204) via an output terminal. Aninput signal A which is a 2-valued digital signal is connected to theinput of each of the switch circuits via a buffer circuit (304 b) and aninverter circuit (303) with enable terminals. The speaker drivingcircuit (300 b) has one of 3-valued states (−1, 0, 1) according to thestate of the input signals A and B. This type of circuit is generallycalled an H bridge circuit.

A PMOS and an NMOS which are complementary MOS transistors are used inthe type of switch circuit shown in FIG. 3 a and FIG. 3 b. However, itis possible to form the switch circuit using only NMOS transistors oronly PMOS transistors. In addition, it is possible to form the switchcircuit using a switching element which uses a semiconductor other thana MOS transistor.

In an embodiment of a digital speaker apparatus, which is shown in FIG.2 a to FIG. 2 c, including a ΔΣ modulator, a post filter circuit, aplurality of speaker driving circuits and driving elements, because aplurality of transmission signals are required after the ΔΣ modulator,it is preferred that the ΔΣ modulator, the post filter circuit, and theplurality of speaker driving circuits are formed as one unit in order toreduce the number of required wires. It is possible to reduce the numberof required signal wires by forming a digital signal processing circuitincluding the ΔΣ modulator, the post filter circuit, the plurality ofspeaker driving circuits and driver elements as one part on asemiconductor or by sealing in the same package.

Fourth Embodiment

A fourth embodiment of a digital speaker apparatus including a ΔΣmodulator, a post filter circuit, a plurality of speaker drivingcircuits and driving elements is shown in FIG. 4 a (a back surface view)and FIG. 4 b (side surface view) as an embodiment of a system includinga digital speaker driving apparatus (400), which is formed with a ΔΣmodulator and a post filter circuit as one unit formed on asemiconductor or sealed in the same package, and a digital speakerapparatus (402) including a plurality of speaker driving elements. A 1bit digital input signal (403) is input into the digital speaker drivingapparatus (402) housing the ΔΣ modulator, the post filter circuit, thedriving circuit of a plurality of digital signals, and a plurality ofdigital speaker driving signals (401) are output. A power supply line(404) supplies a power to the digital speaker driving circuit (402). Thedigitals speaker driving circuit (402) is arranged near the speakerdriving elements so that the distance between the plurality of digitalspeaker driving signals (401) and speaker driving elements becomessmaller. It is possible to make the wiring distance as small as possibleby arranging the digital speaker driver circuit (402) immediately behindthe speaker as is shown in FIG. 4 a and FIG. 4 b.

As stated above, according to the first to fourth embodiments of thepresent invention, a digital input signal which is input to a digitalspeaker apparatus is not converted even once into an analog signalwithin the digital speaker apparatus, and by driving a plurality ofspeaker driving elements by a plurality of digital signals, it becomespossible to directly convert a digital signal into an analog audio. AnA/D convertor circuit necessary for the analog conversion is notrequired because a digital signal is not converted to an analog signalin the apparatus, and a reduction of power consumption and of a requiredsemiconductor area is possible and a low cost digital speaker apparatuscan be provided. Because the digital speaker apparatus can output alarge sound pressure with a low driving voltage, in the case where adigital signal process circuit is formed monolithically on asemiconductor, it is not necessary to use a special semiconductortechnology for handling a high voltage, and it is possible to provide anintegrated digital speaker driving apparatus necessary for a digitalspeaker apparatus using a low voltage semiconductor technology.Electromagnetic irradiation (EMI) is small because of driving with a lowvoltage and it is possible to reduce the costs of suppressingelectromagnetic irradiation. Because there is no A/D (D/A) convertorbetween a digital signal source and digital speaker apparatus, it ispossible to avoid a deterioration in sound quality.

Fifth Embodiment

FIG. 5 shows a fifth embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. A 1 bit digital input signal (510) is input to the ΔΣmodulator (501) and converted to a plurality of n bit digital signals(511) by the ΔΣ modulator (501). The plurality of n bit digital signalsare converted to m number of digital signals (512) which have beenmiss-match shaped by a post filter (502). The m number of digitalsignals drive s number of driving elements (5041-504 s) by speakerdriving circuits (5031-503 s) and an analog audio is directly convertedby vibration membranes (513). The ΔΣ modulator (501), a post filtercircuit (502), the speaker driving circuits (5031-503 s), and a powercircuit (505) which supplies a power to these circuits are structuralcomponents of the digital speaker apparatus (500). In the presentembodiment, s number of driving elements which are combined drive aplurality (2) of speaker vibration membranes (513 a, 513 b). Anarbitrary combination is possible between the number of driving elements(s) and the number of speaker vibration membranes (r), as long as acircuit outputting a plurality of digital signals by a ΔΣ modulator anda post filter directly coverts into an analog audio by driving aplurality of speaker elements. Generally, it is sufficient that s>1 andr≧1.

Sixth Embodiment

FIG. 6 shows a sixth embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. A 1 bit digital input signal (610) is input to a ΔΣ modulator(601) and converted to a plurality of n bit digital signals (611) by theΔΣ modulator (601). The plurality of n bit digital signals (611) areconverted to m number of digital signals (612) which have beenmiss-match shaped by a post filter (602). The m number of digitalsignals drive s number of driving elements (6041-604 s) by speakerdriving circuits (6031-603 s) and a vibration membrane (613) directlyconverts into analog audio. The ΔΣ modulator (601), the post filtercircuit (602), speaker driving circuits (6031-603 s) and the powercircuit (605) which supplies a power to these circuits are structuralcomponents of the digital speaker apparatus (600).

In the present embodiment, a plurality of coils are bunched together andwound so that s number of driving elements together drive speakervibration membrane (613). In the case of winding a plurality of coils, aplurality of coil wires may be twisted (604 a) and wound or they may belined up (604 b) and wound. In addition, a single part of a coil mayalso be separated. An arbitrary arrangement of the plurality of drivingelements required for the digital speaker apparatus is possible.

Seventh Embodiment

FIG. 7 shows a seventh embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. A 1 bit digital input signal (710) is input to a ΔΣ modulator(701) and converted to a plurality of n bit digital signals (711) by theΔΣ modulator (701). The plurality of n bit signals are converted to mnumber of digital signals (712) which have been miss-match shaped by apost filter (702). The m number of digital signals drive s number ofdriving coils (7041-704 s) by driving circuits (7031-703 s) and generatea magnetic field to a magnetostrictor (713). An audio signal is directlyconverted by a driving part (714) which is mechanically connected withthe magnetostrictor (713). The ΔΣ modulator (701), the post filtercircuit (702), the speaker driving circuits (7031-703 s) and a powercircuit (705) which supplies a power to these circuits are structuralcomponents of the digital speaker apparatus (700).

In the present embodiment, a plurality of coils are wound so that snumber of driving elements drive the driving part (714) which ismechanically connected with the magnetostrictor (713). The size of themagnetostrictor (713) changes at a speed of nsec-μsec according to anexternal magnetic field caused by a coil or a magnet. It is possible torealize a bone conduction digital speaker apparatus (700) if amagnetostrictor (713) is used instead of an ordinary voice coil. Otherthan the bone conduction digital speaker apparatus (700) the presentembodiment can also be applied to the digital control of an injectionvalve, a pump, a positioner, an actuator such as a linear actuator, anda sensor such as a torque sensor among vehicle parts.

Eighth Embodiment

An eighth embodiment of a digital speaker apparatus system including acircuit which outputs a plurality of digital signals by a ΔΣ modulatorand a post filter circuit, and a plurality of speaker driver elements isshown in FIG. 8 a to FIG. 8 c. A 1 bit digital input signal (810) isinput to a ΔΣ modulator (801) and converted to a plurality of n bitdigital signals (811) by the ΔΣ modulator (801). The plurality of n bitsignals are converted to m number of digital signals (812) which havebeen miss-match shaped by a post filter (802). The m number of digitalsignals drive s number of electrostatic elements (8041-804 s) by drivingcircuits (8031-803 s) and an audio signal is obtained. The ΔΣ modulator(801), post filter circuit (802), speaker drive circuits (8031-803 s),and a power circuit (805) which supplies a power to these circuits arestructural components of the digital speaker apparatus (800).

FIG. 8 b shows an embodiment wherein the ΔΣ modulator (801), a postfilter circuit (802), and four electrostatic elements (8041-8044) areformed monolithically on the same substrate. This type of integrateddigital speaker apparatus (820) can be realized by manufacturing adigital circuit and an electrostatic speaker element on the same siliconsubstrate using a silicon process technology, for example, and theintegration into a headphone apparatus (830) which uses the type ofdigital speaker apparatus shown in FIG. 8 c is easy.

Ninth Embodiment

FIG. 9 a shows a ninth embodiment of a digital speaker apparatus systemincluding a circuit which outputs a plurality of digital signals by a ΔΣmodulator and a post filter circuit, and a plurality of speaker drivingelements. A 1 bit digital input signal (910) is input to a ΔΣ modulator(901) and converted to a plurality of n bit digital signals (911) by theΔ Σ modulator (901). The plurality of n bit signals are converted to mnumber of digital signals (912) which have been miss-match shaped by apost filter (902). The m number of digital signals drive s number ofspeakers (9041-904 s) by driving circuits (9031-903 s) after a delay isindividually controlled by a digital delay control circuit (905)controlled by a digital signal (920), and an audio signal is obtained.The ΔΣ modulator (901), the post filter circuit (902), the speaker drivecircuits (9031-903 s), and a power circuit (905) which supplies a powerto these circuits is a structural component of the digital speakerapparatus (900).

FIG. 9 b shows an embodiment of the digital speaker apparatus (900) inthe case where the ΔΣ modulator (901), a post filter circuit (902),speaker driving circuits (9031-903 s), and the power source circuit(906) which supplies a power to these circuits are connected to a largescreen flat display television (930). A plurality of speakers arearranged on the top side, the bottom side, the left side, and the rightside of the flat television and it is possible to change thedirectionality of a play back sound by controlling the delay of signalswhich drive each of the speakers. For example, if the delay times ofdigital signals to a plurality of speakers of the digital speakerapparatus (900) are controlled by a signal from a home game console(940), it is possible to increase the realistic sensation of the game bydirecting the audio to the top, the bottom, the left, or the rightaccording to the contents of the game.

Similarly, if the delay times of digital signals to the plurality ofspeakers of the digital speaker apparatus (900) are controlled by asignal from a remote control of the flat screen television, thedirectionality of the play back sound can be focused in the central partof the screen, or the play back sound may be made to have nodirectionality so that play back sound can be heard throughout a roomaccording to the contents of the program being watched.

It is possible to manufacture a digital acoustic system with a digitalspeaker apparatus, as shown in the first to the ninth embodiments, byinputting a signal of a digital signal source as a digital signal to adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements and a plurality of speakers.

Tenth Embodiment

FIG. 10 shows a tenth embodiment of a digital acoustic system with adigital speaker apparatus (1002) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driver elements, and a plurality ofspeakers, to which a digital signal from a mobile digital sound sourceplay back apparatus as a digital signal source (1003) is connected(1001) and which directly converts to an analog audio without convertingan input digital signal to an analog signal. In the present embodiment,a battery (1004) is used as a power source supplied to the digitalspeaker apparatus. However, it is possible to supply power from aseparate external power source.

Eleventh Embodiment

FIG. 11 shows an eleventh embodiment of a digital acoustic system with adigital speaker apparatus (1102) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driving elements and a plurality ofspeakers, to which a digital signal from a mobile phone device as adigital signal source (1103) is connected (1101) and which directlyconverts to an analog audio without converting an input digital signalto an analog signal. A headphone type digital speaker apparatus is usedas the digital speaker apparatus in the present embodiment. However, itis possible to use an arbitrary digital speaker apparatus other thanheadphones.

Twelfth Embodiment

FIG. 12 shows a twelfth embodiment of a digital acoustic system with adigital speaker apparatus (1202) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driving elements, and a plurality ofspeakers, to which a digital signal from a personal computer as adigital signal source (1203) is connected and, which directly convertsto an analog audio without converting an input digital signal to ananalog signal. A digital speaker apparatus arranged with a plurality ofcoils on one vibration membrane is used in the present embodiment.However, it is possible to use a digital speaker apparatus arranged witha plurality of speakers.

Thirteenth Embodiment

FIG. 13 shows a thirteenth embodiment of a digital acoustic system witha digital speaker apparatus (1302) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driving elements and a plurality ofspeakers, to which a digital signal from an active noise control digitalaudio processing apparatus as a digital signal source (1303) isconnected and which directly converts to an analog audio withoutconverting an input digital signal to an analog signal. A signal whichcancels peripheral noise from a sound collecting microphone (1304) iscalculated by a digital audio processing apparatus, and by inputting tothe digital speaker apparatus (1302) it is possible to manufacture a lowpower consumption active noise control digital acoustic system. It isalso possible to apply the present embodiment to a television phone or aremote conference echo cancelling digital acoustic system. It is alsopossible to apply the present embodiment to a digital acoustic systemfor a delay control of a large scale amplifier in a concert hall or asports ground.

Fourteenth Embodiment

FIG. 14 shows a fourteenth embodiment of a digital acoustic system witha digital speaker apparatus (1402) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driving elements and a plurality ofspeakers, to which a digital signal from a mobile phone device via awireless communication technology (Bluetooth etc) as a digital signalsource (1403) is connected (1401) and which directly converts to ananalog audio without converting an input digital signal to an analogsignal. A headphone type digital speaker apparatus is used as thedigital speaker apparatus in the present embodiment. However, it ispossible to use an arbitrary digital speaker apparatus other thanheadphones. In addition, in the present embodiment, an example using amobile phone device as the digital signal source (1403) is shown.However, the present embodiment can also be applied to an arbitrarydigital acoustic system which connects a digital signal to the digitalspeaker apparatus (1402) from a digital signal source via a wirelesscommunication technology.

Fifteenth Embodiment

FIG. 15 a shows a fifteenth embodiment of a system configuration of adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driver elements. A 1 bit digital input signal(1510) is input to a ΔΣ modulator (1501) and converted to a plurality ofn bit digital signals (1511) by the ΔΣ modulator (1051). The pluralityof n bit signals are converted to m number of digital signals (1512 a)by a formatter (1502 a) and converted to m number of digital signals(1512 b) which have been miss-match shaped by a filter (1502 b). The mnumber of digital signals drive s number of driving elements (15041-1504s) by speaker driving circuits (15031-1503 s) and an analog signal isdirectly converted by a vibration membrane (1513). The Δ Σ modulator(1501), the formatter (1502 a), the filter (1502 b), speaker drivecircuits (15031-1503 s) and a power circuit (1505) which supplies apower to these circuits are structural components of the digital speakerapparatus (1500).

The structural components of a filter circuit (1502 b) used in thepresent embodiment are shown in FIG. 15 b. In order to performmiss-match shaping, the m number of digital signals (1512 a), which areinput to a selection circuit (1505), are selected in order of low usagefrequency by calculating the usage frequency of the m number of digitalsignals of the selection circuit using an integration circuit (1506 a)and an integration circuit (1506 b), which are formed by delay elementsand adders.

Sixteenth Embodiment

FIG. 16 shows a sixteenth embodiment of a system configuration of adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements. The structural components of thefilter circuit (1602 b) used in the present embodiment are shown. Inorder to perform miss-match shaping, the m number of digital signals(1612 a), which are input to a selection circuit (1605), are selected inorder of low usage frequency by calculating the usage frequency of the mnumber of digital signals of the selection circuit using n stages ofintegration circuits (16061-1606 n), which are formed by delay elementsand adders. In the present embodiment, the filter circuit can be formedby an arbitrary number of stages of integration circuits of one stage ormore.

Seventeenth Embodiment

FIG. 17 a shows a seventeenth embodiment of a system configuration of adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements having 3-valued switchingamplifiers. A 1 bit digital input signal (1710) is input to a ΔΣmodulator (1701). The ΔΣ modulator (1701) converts the digital inputsignal to a plurality of n bit digital signals (1711). The plurality ofn bit signals are converted to m number of digital signals (1712 a) by aformatter (1702 a) and converted to m number of digital signals (1712 b)which have been miss-match shaped by a filter (1702 b). The speakerdriving circuits (17031-1703 s) directly generate an analog audio by avibration membrane (1713) by driving s number of driving elements(17041-1704 s) to each of which a part of the m number of digitalsignals are input. Furthermore, the driving elements (17041-1704 s) areformed from s number of 3-valued switching amplifiers. The ΔΣ modulator(1701), the formatter (1702 a), the filter (1702 b), the speaker drivecircuits (17031-1703 s) which are formed from 3-valued switchingamplifiers, and a power circuit (1705) which supplies a power to thesecircuits are structural components of the digital speaker apparatus(1700).

For example, in the case where s=8, let us suppose that a digitalspeaker apparatus is formed by 8 speaker driving circuits each having a3-valued switching amplifier. Each driving device can hold a 3-valuedstate among −1, 0, and +1. Therefore, because the speaker device circuitincluding 8 3−valued switching amplifiers can hold −8, −7, . . . −1, 0,+1, . . . +7, +8 (=17) states, the number of bits of a digital signal(1712 a) output by the formatter (1702 a) becomes m=17. Similarly,because the number of bits required to express m=17 states in binary is5 bits, it is sufficient to prepare a ΔΣ modulator (1701) which convertsa 1 bit digital input signal (1710) into an n=5 bit digital signal(1711).

FIG. 17 b shows an embodiment of a speaker driving circuit including a3-valued switching amplifier. In FIG. 17 b, a circuit of a speakerdriving circuit 1703 s is shown as an example among circuits from 17031to 1703 s. The speaker driving circuit 1703 s includes a first and asecond source transistor 301 and a first and a second sink transistor.The first source transistor and the first sink transistor are connectedin series and an input signal A is input to each gate. In addition, thesecond source transistor and the second sink transistor are connected inseries and an input signal /A is input to each gate. In addition, eachof the connection points of the first source transistor and the firstsink transistor, and the connection points of the second sourcetransistor and the second sink transistor are connected to a digitalsignal terminal, two of which form a pair, of a digital speaker.Furthermore, this type of circuit is generally called an H bridgecircuit in the field of motor control.

As is shown in the chart of FIG. 17 b, the speaker driving circuit (1703s) holds 3-valued states (−1, 0, +1) according to the state of inputsignals /A and A. Furthermore, generally, /A expresses the inverse of A,however, in the present embodiment, /A and A sometimes have the samevalue.

In the digital speaker apparatus system including a circuit whichoutputs a plurality of digital signals by a ΔΣ modulator and a postfilter circuit, and a plurality of speaker driving elements having3-valued switching amplifiers, as shown in FIG. 17 a and FIG. 17 b, thespeaker driving circuit (1700 b) can be configured so that the number of0 states increases when the amplitude of a digital signal which is inputis small, wasteful switching operations can be avoided, and a low powerconsumption digital speaker apparatus can be realized. Simultaneously,noise and electromagnetic radiation caused by a switching operation canbe reduced.

Eighteenth Embodiment

FIG. 18 shows an eighteenth embodiment of a system configuration of adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements having 3-valued switchingamplifiers. A 1 bit digital input signal (1810) is input to the ΔΣmodulator (1801) and the Δ Σ modulator (1801) converts the digital inputsignal to a plurality of n bit digital signals (1811). The plurality ofn bit signals are converted to m number of digital signals (1812 a) by aformatter (1802 a) and converted to m number of digital signals (1812 b)which have been miss-match shaped by a filter (1802 b). The speakerdriving circuits (18031-1803 s) drive s number of drive elements(18041-1804 s) to each of which a part of the m number of digitalsignals is input, and an analog audio is directly generated by avibration membrane (1813). Furthermore, the driving elements (18041-1804s) are formed from s number of 3-valued switching amplifiers.

A 1 bit digital input signal (1810) is also input to a peak detector(1806) and a control signal (1816) is output according to the amplitudevalue of the digital input signal. The peak detector (1806) calculatesthe amplitude value of audio which the digital input signal representsand the control signal (1816) is output according to the result of thiscalculation. For example, the amplitude value is calculated as theloudness of audio during a certain length. The control signal (1816) isinput to the formatter (1802 a). The formatter (1802 a) controls changeof the number of bits of the digital signal (1812 a) which is input tothe filter (1802 b) up to the maximum m bits according to the amplitudevalue. That is, if the amplitude value is 0 or small, the digital signal(1812 a) with 0 bits or a number of bits close to 0 is output by theformatter, and if the amplitude value is large, the digital signal (1812a) with a number of bits close to m is output by the formatter.Furthermore, for example, the number of bits of the digital signal (1812a) is calculated except a signal which keeps the same value during acertain time period.

The ΔΣ modulator (1801), the formatter (1802 a), the filter (1802 b),the speaker drive circuits (18031-1803 s) which are formed from a threelevel switching amplifier, the peak detector (1806) and their circuitsare a structural component of the digital speaker apparatus (1800).

As stated above, a system of dynamically controlling the number of bitsof a digital signal which is input to a filter according to theamplitude of the digital signal which is input, the system including adigital speaker apparatus having a circuit which outputs a plurality ofdigital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements having 3-valued switchingamplifiers and also including a peak detector is explained withreference to FIG. 18. In this type of system, because the number ofunits for miss-match shaping in the filter which operates is small whenthe amplitude of a digital signal which is input is small, the range ofcharacteristic variations of the units becomes smaller. Consequently,because it is possible to effectively control noise, it is possible torealize a digital speaker apparatus which can play back high qualityaudio. Simultaneously, noise and electromagnetic radiation caused by aswitching operation can be reduced.

Nineteenth Embodiment

FIG. 19 shows a nineteenth embodiment of a system configuration of adigital speaker apparatus including a circuit which outputs a pluralityof digital signals by a ΔΣ modulator and a post filter circuit, and aplurality of speaker driving elements having 3-valued switchingamplifiers. A 1 bit digital input signal (1910) is input to a serialparallel convertor (1901 a) and the serial parallel convertor (1901 a)converts the digital input signal to a p bit digital audio signal (1911a). For example, in the case where the 1 bit digital input signal (1910)is obtained by play back of audio data recorded in a compact disc (CD),conversion to a 16 bit digital audio signal is preferred. In order toremove an unnecessary outside band of folding frequency component whenthe p bit digital audio signal (1911 a) is over sampled by the ΔΣmodulator (1901 c), the p bit digital audio signal (1911 a) is input toan interpolation filter (1901 b) and a q bit digital audio signal (1911b) is output. The q bit digital audio signal (1911 b) is over sampled bythe ΔΣ modulator (1901 c) and converted to a plurality of n bit digitalsignals (1911 c) by the ΔΣ modulator (1901 c). In the presentembodiment, the relationship of n<p and q and n>2 holds. The pluralityof n bit digital signals are converted to m number of digital signals(1912 a) by the formatter (1902 a). The m number of digital signals(1912 a) are input to the formatter (1902 a) and converted to m numberof digital signals (1912 b) which have been miss-match shaped. Thespeaker driving circuits (19031-1903 s) drive number of drive elements(19041-1904 s) to each of which a part of m number of digital signalsare input, and an analog audio is directly converted by a vibrationmembrane (1913). Furthermore, the driving elements (19041-1904 s) areformed from s number of 3-valued switching amplifiers. The Δ Σ modulator(1901), the formatter (1902 a), the filter (1902 b), the speaker drivecircuits (19031-1903 s) which are formed from 3-valued switchingamplifiers, and a power circuit (1905) which supplies a power to thesecircuits are structural components of the digital speaker apparatus(1900).

As is shown in the nineteenth embodiment, a 1 bit digital signal inputwithin the Δ Σ modulator (1901 c) shown in the first to the eighteenthembodiments is converted to a p bit digital audio signal (1911 a) by theserial parallel convertor (1901 a). In addition, there may be a case inwhich the interpolation filter (1901 b) is inserted in order to removean unnecessary outside band of folding frequency component when the pbit digital audio signal is over sampled. These structural componentsare not essential components of the present invention. In the first toeighteenth embodiments, a 1 bit signal is input to a ΔΣ modulator.However, actually, it is possible to represent a digital audio signalhaving an arbitrary number of bits by the 1 bit digital signal. Forexample, the standard 16 bits in the case of a CD, and the standard 24bits as well as 16 bits in case of a DVD are established.

It is possible to input a digital signal which can represent a digitalaudio signal having an arbitrary number of bits to a ΔΣ modulator, whichis a structural component of the present invention. At this time, it isone of characteristics of the present invention that the number of bitsof a digital signal which is output from the ΔΣ modulator is less thanthe number of bits of a digital audio signal which is input to the ΔΣmodulator. Consequently, it is possible to decode an audio signal byless speaker drive circuits than an amplitude gradient of audio which isrepresented by the number of bits of a digital signal.

For example, in the case where a 16 bit audio signal is to be faithfullyplayed back, it is possible to play back an audio in the same or higherquality than the conventional technology with about 8 units in thepresent embodiment whereas in the conventional technology, 2¹⁶−1=65535units are necessary.

As stated above, according to the present invention, because it ispossible to decode an audio signal by directly driving less speakerdriving circuits than the amplitude gradient of audio by a digital audiosignal, it is possible to significantly reduce the costs required for adigital audio demodulation. It becomes easy to provide directionalityacoustic effects using a plurality of speaker drive circuitssimultaneously.

Twentieth Embodiment

FIG. 20 shows a twentieth embodiment of a digital acoustic systemwherein a digital speaker apparatus (2001) including a circuit whichoutputs a plurality of digital signals by a ΔΣ modulator and a postfilter circuit, a plurality of speaker driving elements, and a pluralityof digital speakers, and a digital commercial display device (2002) arecombined and the digital speaker apparatus is connected to a controlapparatus (2004) which controls the directionality of the digitalspeaker apparatus (2001) according to a signal from a sensor apparatus(2003).

In the present embodiment, as in the ninth to the fourteenthembodiments, a plurality of speakers are used and the delays of signalseach of which drives each speaker are controlled by a digital delaycircuit as in the ninth embodiment. Consequently, the directionality ofa play back sound can be changed so that it is directed towards theexistence direction or location of a person or an object which isdetected.

The sensor apparatus (2003) detects a certain peripheral information.For example, the sensor apparatus (2003) is a camera device and aphotographed image around the periphery of the sensor (2003) is taken.By analyzing a photographed image, the existence of a person or anobject in the periphery of the sensor apparatus (2003) is detected. Inaddition, it is also possible to detect the direction and location of aperson or an object. In this case, it is possible to detect thedirection and location more accurately by using the information detectedby a plurality of sensor apparatuses (2003). In addition, the sensorapparatus (2003) may be an infra red sensor. In this case, infra redgenerated by heat of a person or an object is detected and the presence,direction and location of a person or an object are calculated accordingto the detection result. In addition, not only electromagnetic waveswhich include light but also ultrasonic sound waves generated from thedigital speaker apparatus (2001) and reflected by a person or an objectmay be detected. In addition, by arranging a switch on the surface of aroad or a floor and it is possible to detect the position of a person orobject according to On/Off of the switch.

The detection result of the sensor apparatus (2003) is analyzed by thecontrol apparatus (2004) such as a micro computer, and may be used inthe control of the digital speaker apparatus (2001) and/or the digitalcommercial display device.

In the present embodiment, by digitally applying a delay to a signalfrom the ΔΣ modulator and the formatter using a delay circuit, the phaseshift of a signal to each driving device is controlled by the detecteddirection and location. As a result, it is possible to change thedirectionality of an acoustic signal emitted in space. For example, inthe speaker apparatus (2001), three speakers SP1, SP2, and SP3 arearranged in this order in one line at equal intervals. At this time, inthe case where the distance between speakers is d, the wavelength of asignal is λs, and the angle of deviation is θ when the front of thespeaker apparatus (2001) is 0 radian, if the phase of SP2 with respectto SP3 is delayed by (2 π d sin θ)/λs, and the phase of SP1 is (4 π dsin θ)/λs, it is possible to realize a directionality to the side of SP1by θ.

It is possible to dynamically control the directionality of an audioplayed back by a digital speaker according to the information detectedby the sensor apparatus (2003). That is, control is performed so that anaudio is emitted in the direction of a location where the object whichtransmits audio of a person etc. exists within a certain range. Thecommercial display device of the present invention can effectivelytransmit audio information which is needed only for the object which hasan interest in a commercial media, and because it is unnecessary to playback audio data at an unnecessary high volume it is possible to managethe noise problem. The present embodiment can also be applied to anexhibition explanation device such as in an art gallery or a sciencemuseum, a display device within a station, an airport, or a hotel, anotice display in public transport such a bus or a train, a premisesguidance device such as a hospital or a city office, as well as adigital commercial display.

Twenty-First Embodiment

FIG. 21 a shows a twenty-first embodiment of a digital acoustic systemfor a vehicle including a digital speaker apparatus (2103) wherein thedigital speaker apparatus (2103) including a circuit which outputs aplurality of digital signals by a ΔΣ modulator and a post filtercircuit, a plurality of speaker driving elements, and a plurality ofspeakers, and a display apparatus (2102) are combined and the digitalspeaker apparatus is configured to control the directionality. In thecase of a digital speaker apparatus for a vehicle, when a rear projectoris used as a display device which is mainly applied as an entertainmentdevice (a DVD or TV device) to passengers sitting in the rear seat, itis necessary to reduce the volume to the driver depending on thesituation for safety purposes. Because it is possible to dynamicallycontrol the directionality of an audio which is played back by thedigital speaker of the present invention, it can also be widely appliedfor use in vehicles.

The situation stated above is judged based on the detection of avibration or an acceleration by a vibration sensor or an accelerationsensor attached to the vehicle body. For example, the sensor judgeswhether there is a change which exceeds the size of a continuousacceleration when sharp bends continue. In addition, sound external tothe vehicle is detected by a microphone and the sensor judges thepresence of a siren of an emergency or a warning sound of a traincrossing etc. If the sensor judges that sharp bends continue or a sirenis detected, the audio of the entertainment device is controlled so thatthe volume is reduced as much as possible to the driver in order toallow the driver to concentrate on driving. In addition, the currentposition can be detected by using a GPS (Global Positioning System),whether the vehicle is travelling a dangerous route such as a mountainroute can be judged, and the audio of the entertainment device iscontrolled so that the volume is reduced as much as possible to thedriver in order to allow the driver to concentrate on driving.

As stated above, in order to monitor information external to a vehicleand construct a corresponding vehicle acoustic environment, a monitorcamera (2104) etc. for monitoring the exterior of the car is arrangedand is connected to a central control device (2105) and to a vehicleinterior LAN (2106) to transmit a digital (optical) signal as shown inFIG. 21 b. Information detected by the monitor camera (2104) etc. isanalyzed by the central control device (2105) and a digital speaker iscontrolled based on the result of the analysis. The digital speaker ofthe present invention can control not only volume but also acousticcharacteristics such as directionality via a digital signal. Inaddition, because a digital signal is used, it is possible to easilyconnect to the vehicle interior LAN (2106). Therefore, by connecting thedigital speaker of the present invention to the vehicle interior LAN(2106) it is possible to provide a comfortable and safe vehicle for thedriver and passengers.

In the present embodiment, the digital speaker of the present inventioncan be used not only for entertainment but also as an active noisecancelling device in order to reduce road noise. That is, road noise isdetected by a microphone which is not shown in the diagram and audiowith an opposite phase is generated. In addition, by controllingdirectionality at this time it is possible, for example, to reduce onlythe noise which is audible to the driver or reduce only the noise whichis audible to a side and rear passenger. The present embodiment can beapplied not only to a vehicle digital system but also to an airplane, amotorcycle, a bus, or trains. In addition, the present embodiment can beapplied to a digital acoustic system or a noise cancelling device suchas in a bed or an audio visual room of a capsule hotel or a concerthall.

To summarize the above, for example, a digital speaker driving apparatusis provided which drives a digital speaker having s number of digitalsignal terminals, the digital speaker driving apparatus including: a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal; s number of driving circuits to each of which one partof the m bit digital signal is input and each of which outputs a digitalsignal; and a power circuit which supplies power to the ΔΣ modulator,the post filter, and the s number of driving circuits, wherein the snumber of driving circuits correspond to the s number of digital signalterminals.

As the first digital speaker driving apparatus, a second digital speakerapparatus is provided including a power circuit which supplies avariable voltage to the s number of driving circuits so that amplitudesof outputs of digital signals of the s number of driving circuits areadjusted.

As the first digital speaker driving apparatus, a third digital speakerdriving apparatus is provided which includes a digital attenuator whichadjusts the volume of the digital speaker by performing a predeterminedcalculation process on the digital input signal and inputting the signalto the ΔΣ modulator.

As the first or the second digital speaker driving apparatus, a fourthdigital speaker drive apparatus is provided in which the power circuitis controlled according to the digital input signal.

As a digital speaker driving apparatus which is connected to digitalsignal terminals of a digital speaker, a fifth digital speaker drivingapparatus is provided which includes a first output circuit connected toa first input terminal of the digital terminals of the digital speaker;and a second output circuit connected to a second input terminal of thedigital terms of the digital speaker, the second input terminal forminga pair with the first input terminal; wherein the first output circuitand the second output circuit are input with signals, the signals beingthe inverse of each other.

As the fifth digital speaker driving apparatus, a sixth digital speakerdriving apparatus is provided wherein the first output circuit and thesecond output circuit output signals of a first voltage, a secondvoltage, or a third voltage, in the case where the first output circuitoutputs the first voltage and the second output circuit outputs thethird voltage, the state of the digital signal output is in a firststate, in the case where the first output circuit outputs the thirdvoltage and the second output circuit outputs the first voltage, thestate of the digital signal output is in a second state, and in the casewhere both of the first output circuit and the second output circuitoutput the second voltages, the state of the digital signal output is ina third state.

As the first digital speaker driving apparatus, a seventh digitalspeaker driving apparatus is provided wherein the ΔΣ modulator, the postfilter, and the s number of driving circuits are formed on a singlesemiconductor or are sealed in a single package.

An eighth digital speaker apparatus is provided which includes a digitalspeaker which has a plurality of input terminals; and a digital speakerdriving circuit which is connected to the input terminals and drives thedigital speaker; wherein the digital speaker driving circuit is arrangedjust behind coils the digital speaker

A ninth digital speaker apparatus is provided which includes a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal; s number of driving circuits to each of which one partof the m bit digital signal is input and each of which outputs a digitalsignal; number of speaker driving elements each of which is driven bycorresponding driving circuit among the s number of driving circuits;and r number of vibration membranes which are driven by the s number ofdriving elements; wherein s and r are 2 or more.

A tenth digital speaker apparatus is provided which includes a Δ Σmodulator and a digital speaker a ΔΣ modulator; and a digital speaker;wherein the digital speaker has a plurality of coils each of which isdriven by a different digital signal and all of which vibrate a commonvibration membrane.

As the tenth digital speaker apparatus, an eleventh digital speakerapparatus is provided wherein the plurality of coils are bound togetherand wound.

A digital actuator is proposed which includes a magnetostrictor, and aplurality of coils which are each driven by different digital signalsand which generate a magnetic field to the magnetostrictor.

A twelfth digital speaker apparatus is provided which includes a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal; s number of driving circuits to each of which one partof the m bit digital signal is input and each of which outputs a digitalsignal; and s number of electrostatic elements each of which is drivenby a corresponding driving circuit among the s number of drivingcircuits.

As the twelfth digital speaker apparatus, a thirteenth digital speakerapparatus is provided wherein the ΔΣ modulator, the post filter, and thes number of driving circuits and the s number of electrostatic elementsare formed on a single substrate.

As a digital speaker driving apparatus which drives a digital speakerhaving s number of digital signal terminals, a fourteenth digitalspeaker apparatus is provided which includes a ΔΣ modulator whichmodulates a digital input signal and outputs an n bit digital signal; apost filter which is connected to the ΔΣ modulator and outputs an m bitdigital signal obtained by miss-match shaping the n bit digital signal;a digital delay control circuit which delays the m bit digital signaland outputs the delayed m bit digital signal; s number of drivingcircuits to each of which one part of the m bit digital signal is inputand each of which outputs a digital signal; wherein a delay time periodof the digital delay control circuit is controlled for each outputaccording to a control signal.

A flat display device is provided which includes a flat display; aplurality of digital speakers which are arranged in a line on at leastone side of the flat display; and a delay control circuit which controlsthe delay time periods of driving signals supplied to the plurality ofdigital speakers according to a control signal.

A fifteenth digital speaker apparatus is provided which includes a portfor connecting to a portable digital audio source apparatus; a circuitfor processing the digital signals input to the port in a digitalformat; and a digital speaker driven by the circuit; wherein the digitalspeaker apparatus operates with a battery.

A first mobile electronic device is provided which includes a digitalspeaker; and a driving apparatus which drives the digital speakerwithout converting a digital signal to an analog signal; wherein theportable electronic device operates with a battery.

A second mobile electronic device is provided which includes a port forconnecting to a portable digital audio source apparatus; a drivingapparatus for processing the digital signals input to the port in adigital format; and a digital speaker driven by the driving apparatus;wherein the portable electronic device operates with a battery.

A digital speaker apparatus is provided which includes a digitalspeaker; a digital speaker driving apparatus for processing a digitalsignal without converting the digital signal to an analog signal; and amicrophone; wherein the digital speaker driving apparatus operates sothat a noise is cancelled based on a signal from the microphone.

A third mobile electronic device is provided which includes a wirelessreceiver receiving a digital signal; a digital speaker driving apparatuswhich generates a plurality digital signals without converting thedigital signal output by the wireless receiver to an analog signal; anda digital speaker which is driven by the plurality of digital signals.

A sixteenth digital speaker driving apparatus is provided in which adigital speaker system which drives the digital speaker drivingapparatus includes a ΔΣ modulator which modulates a digital input signaland outputs an n bit digital signal; a post filter which is connected tothe ΔΣ modulator and outputs an m bit digital signal obtained bymiss-match shaping the n bit digital signal; and s number of drivingcircuits each of which corresponds to one of the s pairs of digitalinput terminals and to each of which one part of the m bit digitalsignal is input and each of which outputs a digital signal; wherein eachof s number of driving circuits has a first output circuit connected toa first input terminal of a corresponding digital input terminal and asecond output circuit connected to a second input terminal which forms apair with the first input terminal of a corresponding digital inputterminal; and wherein the driving circuit has at least three states ofdigital signal output according to the combination of a first digitalsignal input to the first output circuit and a second digital signalinput to the second output circuit.

As the sixteenth digital speaker drive apparatus, a seventeenth digitalspeaker drive apparatus is provided wherein a digital signal which isinput to the ΔΣ modulator is obtained from one bit input signal to p bitby serial/parallel conversion and by oversampling to signals of bits thenumber of which is larger than n and p.

As the seventeenth digital speaker drive apparatus, an eighteenthdigital speaker drive apparatus is provided wherein the driving circuitis in a sate in which the voltage of the first input terminal and thevoltage of the second input terminal become equal when the first digitalsignal and the second digital signal are the same.

In the eighteenth digital speaker drive apparatus, a nineteenth digitalspeaker drive apparatus is provided wherein each of the first outputcircuit and the second output circuit includes a first source transistorand a first sink transistor which are connected in series with the firstdigital signal which is input, and a second source transistor and asecond sink transistor which are connected in series with the seconddigital signal which is input, wherein a connection point between thefirst source transistor and the first sink transistor and a connectionpoint between the second source transistor and the second sinktransistor form an H bridge circuit which is connected to acorresponding digital signal terminal.

In the nineteenth digital speaker drive apparatus, a twentieth digitalspeaker drive apparatus is provided which includes a peak detector whichcalculates an amplitude of audio represented by the digital inputsignal; wherein the post filter controls the number of bits of an outputdigital signal according to the amplitude calculated by the peakdetector.

In the twentieth digital speaker drive apparatus, a twenty-first digitalspeaker drive apparatus is provided wherein the post filter outputs adigital signal with fewer bits the lower the amplitude calculated by thepeak detector.

In the twenty-first digital speaker driving apparatus, a twenty-seconddigital speaker drive apparatus is provided which drives a plurality ofdigital speakers having s number of digital signal terminals, andincludes a ΔΣ modulator which modulates a digital input signal andoutputs an n bit digital signal; a post filter which is connected to theΔΣ modulator and outputs an m bit digital signal obtained by miss-matchshaping the n bit digital signal; a digital delay control circuits whichdelays the m bit digital signal and outputs the delayed m bit digitalsignal; s number of driving circuits to each of which a part of thedelayed m bit digital signal is input and each of which outputs adigital signal; and a sensor which senses information related to aperson or an object which exists in a periphery; wherein a delay timeperiod of the digital delay control circuit is controlled according to acontrol signal generated based on the information sensed by the sensor,and the directionality of audio played back by the plurality of digitalspeakers is controlled to a direction or position of the person or theobject detected by the sensor.

As the twenty-second digital speaker driving apparatus, a twenty-thirddigital speaker driving apparatus is provided wherein the sensor is acamera or an infra read sensor which photographs periphery images.

As the twenty-third digital speaker driving apparatus, a twenty-fourthdigital speaker driving apparatus is provided wherein the sensor is anultrasound sensor.

As the twenty-fourth digital speaker drive apparatus, a twenty-fifthdigital speaker drive apparatus is provided wherein all or one part ofthe plurality of digital speakers generate ultrasound detected by thesensor.

As a digital speaker driving apparatus which drives a digital speakerhaving s number of digital signal terminals, a twenty-fifth digitalspeaker driving apparatus is provided including a ΔΣ modulator whichmodulates a digital input signal and outputs an n bit digital signal; apost filter which is connected to the ΔΣ modulator and outputs an m bitdigital signal obtained by miss-match shaping the n bit digital signal;a digital delay control circuit which delays the m bit digital signaland outputs the delayed m bit digital signal; s number driving circuitsto each of which a part of the delayed m bit digital signal is input andeach of which outputs a digital signal; and a microphone which detects asound in a periphery; wherein an audio of an opposite phase to the sounddetected by the microphone is generated by the digital speaker.

As the twenty-sixth digital speaker driving apparatus, a twenty-seventhdigital speaker driving apparatus is provided wherein another digitalspeaker is arranged, and includes a plurality of digital speakers,wherein the digital delay control circuit outputs m bit digital signalwhich is delayed for each digital speaker by controlling the delay timeperiod of the m bit digital signal input.

1. A digital speaker driving apparatus which drives a digital speakerhaving s number of digital signal terminals, comprising: a ΔΣ modulatorwhich modulates a digital input signal and outputs an n bit digitalsignal; a post filter which is connected to the ΔΣ modulator and outputsan m bit digital signal obtained by miss-match shaping the n bit digitalsignal; s number of driving circuits to each of which one part of the mbit digital signal is input and each of which outputs a digital signal;and a power circuit which supplies power to the ΔΣ modulator, the postfilter, and the s number of driving circuits, wherein the s number ofdriving circuits correspond to the s number of digital signal terminals.2. The digital speaker driving apparatus according to claim 1, furthercomprising: a digital attenuator which adjusts the volume of the digitalspeaker by performing a predetermined calculation process on the digitalinput signal and inputting the signal to the ΔΣ modulator.
 3. Thedigital speaker driving apparatus according to claim 1 wherein the ΔΣmodulator, the post filter, and the s number of driving circuits areformed on a single semiconductor or are sealed in a single package. 4.The digital speaker driving apparatus according to claim 1 wherein thepower circuit supplies a variable voltage to the s number of drivingcircuits so that amplitudes of outputs of digital signals of the snumber of driving circuits are adjusted.
 5. The digital speaker drivingapparatus according to claim 1 wherein the power circuit is controlledaccording to the digital input signal.
 6. A digital speaker drivingapparatus connected to digital terminals of a digital speaker,comprising: a first output circuit connected to a first input terminalof the digital terminals of the digital speaker; and a second outputcircuit connected to a second input terminal of the digital terms of thedigital speaker, the second input terminal forming a pair with the firstinput terminal, wherein the first output circuit and the second outputcircuit are input with signals, the signals being the inverse of eachother.
 7. The digital speaker driving apparatus according to claim 6,wherein the first output circuit and the second output circuit outputsignals of a first voltage, a second voltage, or a third voltage, in thecase where the first output circuit outputs the first voltage and thesecond output circuit outputs the third voltage, the state of thedigital signal output is in a first state, in the case where the firstoutput circuit outputs the third voltage and the second output circuitoutputs the first voltage, the state of the digital signal output is ina second state, and in the case where both of the first output circuitand the second output circuit output the second voltages, the state ofthe digital signal output is in a third state.
 8. A digital speakerapparatus comprising: a digital speaker having a plurality of inputterminals; and a digital speaker driving circuit which is connected tothe input terminals and drives the digital speaker, wherein the digitalspeaker driving circuit is arranged in a neighborhood of coils thedigital speaker.
 9. A digital speaker apparatus comprising: a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal, s number of driving circuits to each of which one partof the m bit digital signal is input and each of which outputs a digitalsignal; and s number of speaker driving elements each of which is drivenby corresponding driving circuit among the s number of driving circuits,wherein the ΔΣ modulator, the post filter, and the s number of drivingcircuits are arranged in the neighborhood of the s number of speakerdriving elements.
 10. A digital speaker apparatus comprising: a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal; s number of driving circuits to each of which one partof the m bit digital signal is input and each of which outputs a digitalsignal; s number of speaker driving elements each of which is driven bycorresponding driving circuit among the s number of driving circuits;and r number of vibration membranes which are driven by the s number ofdriving elements, wherein s and r are 2 or more.
 11. A digital speakerapparatus comprising: a ΔΣ modulator; and a digital speaker, wherein thedigital speaker has a plurality of coils each of which is driven by adifferent digital signal and all of which vibrate a common vibrationmembrane.
 12. The digital speaker apparatus according to claim 11,wherein the plurality of coils are twisted together and wound.
 13. Adigital actuator comprising: a magnetostrictor; and a plurality of coilseach of which is driven by a different digital signal and which generatea magnetic field to the magnetostrictor.
 14. A digital speaker apparatuscomprising: a ΔΣ modulator which modulates a digital input signal andoutputs an n bit digital signal; a post filter which is connected to theΔΣ modulator and outputs an m bit digital signal obtained by miss-matchshaping the n bit digital signal; s number of driving circuits to eachof which one part of the m bit digital signal is input and each of whichoutputs a digital signal; and s number of electrostatic elements each ofwhich is driven by a corresponding driving circuit among the s number ofdriving circuits.
 15. The digital speaker apparatus according to claim14, wherein the ΔΣ modulator, the post filter, and the s number ofdriving circuits and the number of electrostatic elements are formed ona single substrate.
 16. A digital speaker apparatus driving a digitalspeaker having s number digital signal terminals, comprising: a ΔΣmodulator which modulates a digital input signal and outputs an n bitdigital signal; a post filter which is connected to the ΔΣ modulator andoutputs an m bit digital signal obtained by miss-match shaping the n bitdigital signal; a digital delay control circuit which delays the m bitdigital signal and outputs the delayed m bit digital signal; and snumber of driving circuits to each of which one part of the m bitdigital signal is input and each of which outputs a digital signal,wherein a delay time period of the digital delay control circuit iscontrolled for each output according to a control signal.
 17. Thedigital speaker apparatus according to claim 16, wherein each of the snumber of driving circuits has a first output circuit connected to afirst input terminal of a digital signal terminal corresponding to eachof the s number of driving circuits and a second output circuitconnected to a second input terminal which forms a pair with the firstinput terminal of the digital terminal; and wherein the driving circuithas at least three states of digital signal output according to thecombination of a first digital signal input to the first output circuitand a second digital signal input to the second output circuit.
 18. Aflat display apparatus comprising: a flat display; a plurality ofdigital speakers which are arranged in a line on at least one side ofthe flat display; and a delay control circuit which controls the delaytime periods of driving signals supplied to the plurality of digitalspeakers according to a control signal.
 19. A digital speaker apparatuscomprising: a port for connecting to a portable digital audio sourceapparatus; a circuit for processing the digital signals input to theport in a digital format; and a digital speaker driven by the circuit,wherein the digital speaker apparatus operates with a battery.
 20. Aportable electronic device comprising: a digital speaker; and a drivingapparatus which drives the digital speaker without converting a digitalsignal to an analog signal, wherein the portable electronic deviceoperates with a battery.
 21. A portable electronic device comprising: aport for connecting to a portable digital audio source apparatus; adriving apparatus for processing the digital signals input to the portin a digital format; and a digital speaker driven by the drivingapparatus, wherein the portable electronic device operates with abattery.
 22. A digital speaker apparatus comprising: a digital speaker;a digital speaker driving apparatus for processing a digital signalwithout converting the digital signal to an analog signal; and amicrophone, wherein the digital speaker driving apparatus operates sothat a peripheral noise is cancelled based on a signal from themicrophone.
 23. A portable electronic device comprising: a wirelessreceiver receiving a digital signal; a digital speaker driving apparatuswhich generates a plurality digital signals without converting thedigital signal output by the wireless receiver to an analog signal; anda digital speaker which is driven by the plurality of digital signals.24. A digital speaker system driving a digital speaker having s pairs ofdigital input terminals, comprising: a ΔΣ modulator which modulates adigital input signal and outputs an n bit digital signal; a post filterwhich is connected to the ΔΣ modulator and outputs an m bit digitalsignal obtained by miss-match shaping the n bit digital signal; and snumber of driving circuits each of which corresponds to one of the spairs of digital input terminals and to each of which one part of the mbit digital signal is input and each of which outputs a digital signal,wherein each of s number of driving circuits has a first output circuitconnected to a first input terminal of a corresponding digital inputterminal and a second output circuit connected to a second inputterminal which forms a pair with the first input terminal of acorresponding digital input terminal, and wherein the driving circuithas at least three states of digital signal output according to thecombination of a first digital signal input to the first output circuitand a second digital signal input to the second output circuit.
 25. Thedigital speaker driving apparatus according to claim 24, wherein adigital signal which is input to the ΔΣ modulator is obtained from onebit input signal to p bit by serial/parallel conversion and byoversampling to signals of bits the number of which is larger than n andp.
 26. The digital speaker driving apparatus according to claim 24,wherein the driving circuit is in a sate in which the voltage of thefirst input terminal and the voltage of the second input terminal becomeequal when the first digital signal and the second digital signal arethe same.
 27. The digital speaker driving apparatus according to claim26, wherein each of the first output circuit and the second outputcircuit includes a first source transistor and a first sink transistorwhich are connected in series with the first digital signal which isinput, and a second source transistor and a second sink transistor whichare connected in series with the second digital signal which is input,and wherein a connection point between the first source transistor andthe first sink transistor and a connection point between the secondsource transistor and the second sink transistor form an H bridgecircuit which is connected to a corresponding digital signal terminal.28. The digital speaker driving apparatus according to claims 24,further comprising a peak detector which calculates an amplitude ofaudio represented by the digital input signal, wherein the post filtercontrols the number of bits of an output digital signal according to theamplitude calculated by the peak detector.
 29. The digital speakerdriving apparatus according to claim 28, wherein the post filter outputsa digital signal with fewer bits the lower the amplitude calculated bythe peak detector.
 30. A digital speaker driving apparatus driving aplurality of digital speakers each having s number of digital signalterminals; a ΔΣ modulator which modulates a digital input signal andoutputs an n bit digital signal; a post filter which is connected to theΔΣ modulator and outputs an m bit digital signal obtained by miss-matchshaping the n bit digital signal; a digital delay control circuits whichdelays the m bit digital signal and outputs the delayed m bit digitalsignal; s number of driving circuits to each of which a part of thedelayed m bit digital signal is input and each of which outputs adigital signal; and a sensor which senses information related to aperson or an object which exists in a periphery, wherein a delay timeperiod of the digital delay control circuit is controlled according to acontrol signal generated based on the information sensed by the sensor,and the directionality of audio played back by the plurality of digitalspeakers is controlled to a direction or position of the person or theobject detected by the sensor.
 31. The digital speaker driving apparatusaccording to claim 30, wherein the sensor is a camera or an infra readsensor which photographs a periphery image.
 32. The digital speakerdriving apparatus according to claim 30, wherein the sensor is anultrasound sensor.
 33. The digital speaker driving apparatus accordingto claim 32, wherein all or one part of the plurality of digitalspeakers generate ultrasound detected by the sensor.
 34. A digitalspeaker driving apparatus driving a digital speaker having s number ofdigital signal terminals, comprising: a ΔΣ modulator which modulates adigital input signal and outputs an n bit digital signal; a post filterwhich is connected to the ΔΣ modulator and outputs an m bit digitalsignal obtained by miss-match shaping the n bit digital signal; adigital delay control circuit which delays the m bit digital signal andoutputs the delayed m bit digital signal; s number driving circuits toeach of which a part of the delayed m bit digital signal is input andeach of which outputs a digital signal; and a microphone which detects asound in a periphery, wherein an audio of an opposite phase to the sounddetected by the microphone is generated by the digital speaker.
 35. Thedigital speaker driving apparatus according to claim 34, furthercomprising another digital speaker, wherein the digital delay controlcircuit outputs m bit digital signal which is delayed for each digitalspeaker by controlling the delay time period of the m bit digital signalinput.